/**
 * $RCSfile$
 * $Revision$
 * $Date$
 *
 * Copyright 2003-2007 Jive Software.
 *
 * All rights reserved. Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.jivesoftware.smack;

import org.jivesoftware.smack.filter.PacketFilter;
import org.jivesoftware.smack.packet.Packet;

import java.util.LinkedList;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.LinkedBlockingQueue;

/**
 * Provides a mechanism to collect packets into a result queue that pass a
 * specified filter. The collector lets you perform blocking and polling
 * operations on the result queue. So, a PacketCollector is more suitable to use
 * than a {@link PacketListener} when you need to wait for a specific result.
 * <p>
 * 
 * Each packet collector will queue up a configured number of packets for
 * processing before older packets are automatically dropped. The default number
 * is retrieved by {@link SmackConfiguration#getPacketCollectorSize()}.
 * 
 * @see Connection#createPacketCollector(PacketFilter)
 * @author Matt Tucker
 */
public class PacketCollector {

	/**
	 * Max number of packets that any one collector can hold. After the max is
	 * reached, older packets will be automatically dropped from the queue as
	 * new packets are added.
	 */
	private int maxPackets = SmackConfiguration.getPacketCollectorSize();

	private PacketFilter packetFilter;
	private LinkedList<Packet> resultQueue;
	private Connection conection;
	private boolean cancelled = false;

	/**
	 * Creates a new packet collector. If the packet filter is <tt>null</tt>,
	 * then all packets will match this collector.
	 * 
	 * @param conection
	 *            the connection the collector is tied to.
	 * @param packetFilter
	 *            determines which packets will be returned by this collector.
	 */
	protected PacketCollector(Connection conection, PacketFilter packetFilter) {
		this.conection = conection;
		this.packetFilter = packetFilter;
		this.resultQueue = new LinkedList<Packet>();
	}

	/**
	 * Creates a new packet collector. If the packet filter is <tt>null</tt>,
	 * then all packets will match this collector.
	 * 
	 * @param conection
	 *            the connection the collector is tied to.
	 * @param packetFilter
	 *            determines which packets will be returned by this collector.
	 * @param maxSize
	 *            the maximum number of packets that will be stored in the
	 *            collector.
	 */
	protected PacketCollector(Connection conection, PacketFilter packetFilter,
			int maxSize) {
		this(conection, packetFilter);
		maxPackets = maxSize;
	}

	/**
	 * Explicitly cancels the packet collector so that no more results are
	 * queued up. Once a packet collector has been cancelled, it cannot be
	 * re-enabled. Instead, a new packet collector must be created.
	 */
	public void cancel() {
		// If the packet collector has already been cancelled, do nothing.
		if (!cancelled) {
			cancelled = true;
			conection.removePacketCollector(this);
		}
	}

	/**
	 * Returns the packet filter associated with this packet collector. The
	 * packet filter is used to determine what packets are queued as results.
	 * 
	 * @return the packet filter.
	 */
	public PacketFilter getPacketFilter() {
		return packetFilter;
	}

	/**
	 * Polls to see if a packet is currently available and returns it, or
	 * immediately returns <tt>null</tt> if no packets are currently in the
	 * result queue.
	 * 
	 * @return the next packet result, or <tt>null</tt> if there are no more
	 *         results.
	 */
	public synchronized Packet pollResult() {
		if (resultQueue.isEmpty()) {
			return null;
		} else {
			return resultQueue.removeLast();
		}
	}

	/**
	 * Returns the next available packet. The method call will block (not
	 * return) until a packet is available.
	 * 
	 * @return the next available packet.
	 */
	public synchronized Packet nextResult() {
		// Wait indefinitely until there is a result to return.
		while (resultQueue.isEmpty()) {
			try {
				wait();
			} catch (InterruptedException ie) {
				// Ignore.
			}
		}
		return resultQueue.removeLast();
	}

	/**
	 * Returns the next available packet. The method call will block (not
	 * return) until a packet is available or the <tt>timeout</tt> has elapased.
	 * If the timeout elapses without a result, <tt>null</tt> will be returned.
	 * 
	 * @param timeout
	 *            the amount of time to wait for the next packet (in
	 *            milleseconds).
	 * @return the next available packet.
	 */
	public synchronized Packet nextResult(long timeout) {
		// Wait up to the specified amount of time for a result.
		if (resultQueue.isEmpty()) {
			long waitTime = timeout;
			long start = System.currentTimeMillis();
			try {
				// Keep waiting until the specified amount of time has elapsed,
				// or
				// a packet is available to return.
				while (resultQueue.isEmpty()) {
					if (waitTime <= 0) {
						break;
					}
					wait(waitTime);
					long now = System.currentTimeMillis();
					waitTime -= (now - start);
					start = now;
				}
			} catch (InterruptedException ie) {
				// Ignore.
			}
			// Still haven't found a result, so return null.
			if (resultQueue.isEmpty()) {
				return null;
			}
			// Return the packet that was found.
			else {
				return resultQueue.removeLast();
			}
		}
		// There's already a packet waiting, so return it.
		else {
			return resultQueue.removeLast();
		}
	}

	/**
	 * Processes a packet to see if it meets the criteria for this packet
	 * collector. If so, the packet is added to the result queue.
	 * 
	 * @param packet
	 *            the packet to process.
	 */
	protected synchronized void processPacket(Packet packet) {
		if (packet == null) {
			return;
		}
		if (packetFilter == null || packetFilter.accept(packet)) {
			// If the max number of packets has been reached, remove the oldest
			// one.
			if (resultQueue.size() == maxPackets) {
				resultQueue.removeLast();
			}
			// Add the new packet.
			resultQueue.addFirst(packet);
			// Notify waiting threads a result is available.
			notifyAll();
		}
	}
}
